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. 2018 Dec 13;8(12):1045.
doi: 10.3390/nano8121045.

Enhancing GaN LED Efficiency through Nano-Gratings and Standing Wave Analysis

Xiaomin Jin  1 , Simeon Trieu  2 , Gregory James Chavoor  3 , Gabriel Michael Halpin  4
Affiliations

Enhancing GaN LED Efficiency through Nano-Gratings and Standing Wave Analysis

Xiaomin Jin et al. Nanomaterials (Basel). .

Abstract

Based on our recent work, this paper reviews our theoretical study on gallium nitride (GaN) light-emitting-diode (LED). The focus of the paper is to improve LED light extraction efficiency through various nano-grating designs. The gratings can be designed at different locations, such as at the top, the middle, and the bottom, on the LED. They also can be made of different materials. In this study, we first present a GaN LED error-grating simulation model. Second, nano Indium Tin Oxide (ITO) top gratings are studied and compared with conventional LED (CLED) using standing wave analysis. Third, we present results related to a patterned sapphire substrate (PSS), SiO₂ Nanorod array (NR), and Ag bottom reflection layer. Finally, we investigate the nano-top ITO grating performance over different wavelengths to validate our design simulation, which focusing on a single wavelength of 460 nm.

Keywords: GaN; LED; nano-grating.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Structure and basic simulation model of conventional Gallium nitride (GaN) based light-emitting-diode (LED).
Figure 2
Figure 2
The schematic diagrams of the top grating simulation, (a) cylindrical pillar grating, (b) conical pillar grating, and (c) cylindrical nano-hole grating. (d) Error grating model: Normal reference grating model and error grating model with both positive and negative shifts.
Figure 3
Figure 3
The schematic diagrams of the top grating simulation of (a) cylindrical pillar grating, (b) conical pillar grating, (c) conventional LED (CLED) with Indium Tin Oxide (ITO) layer, and (d) conventional LED.
Figure 4
Figure 4
LED top output intensity as ITO thickness varies from 0 nm to 450 nm at 1 nm increments.
Figure 5
Figure 5
Light extracted from LED as the grating period is varied. (a) Light extraction from four monitors (top, bottom, left side, and right side) compared with conventional LED (reference 2) for an ITO thickness of 46 nm; (b) total light extraction for difference ITO thicknesses and compared with reference 1 with an ITO of 46 nm and reference 2.
Figure 6
Figure 6
Diagram of LED with a patterned sapphire substrate (PSS), SiO2 NR array, and Ag Reflector. The diagram defines the PSS period (d), PSS width (w), SiO2 NR period (p), SiO2 NR width (a), SiO2 NR high (s), and shows the x and z direction of the LED. (a)–(l) are explained and listed in the paper.
Figure 7
Figure 7
Average power of light extracted in 10 structures, while the PSS width, w = 2.5 μm, and period, d = 3 μm. The SiO2 layer is centered at z = 7.8 μm. Sapphire layer thickness is 80 μm. (a) CLED, (b) CLED with Ag between U-GaN and the sapphire substrate, (c) CLED with Ag below the sapphire substrate, (d) NR, (e) PSS, (f) PSS NR, (g) PSS with Ag between U-GaN and the sapphire substrate, (h) NR with Ag between U-GaN and the sapphire substrate, (i) PSS, Ag below the sapphire substrate, (j) NR array, Ag below the sapphire substrate, (k) PSS NR array with Ag between U-GaN and the sapphire substrate, and (l) LED with PSS, NR array, and Ag below the sapphire substrate.
Figure 8
Figure 8
Average power vs. different sapphire substrate thicknesses with PSS NR and a bottom layer Ag reflector. PSS width of w = 2.5 μm and period of d = 3 μm. SiO2 layer is centered at z = 7.8 μm. (a) Average power extracted against time according to different sapphire substrate thicknesses of 10 μm, 20 μm, 30μm, 40 μm, 50 μm, 60 μm, 70 μm, and 80 μm, and (b) steady state average power.
Figure 9
Figure 9
Total light output for ITO nano-top grating when the free space wavelength is at (a) 450 nm, (b) 460 nm, and (c) 470 nm.
Figure 10
Figure 10
Light extraction intensity across the LED emitting spectrum.
See this image and copyright information in PMC

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